The three #Fediverse software with the widest #groups compatibility are:
(in alphabetical order)
- fedigroups.social - see @hello
- Friendica - find a Friendica server and host there
- Hubzilla - find a Hubzilla server and create your group
The rest have various compatibility issues with other Fediverse software (for years), like group posts/boosts not showing up or your posts not getting boosted or you can't follow the group. This includes #threadiverse software.
If you want to have a true fediverse reach, then choose one from those mentioned above until the other software with federated groups feature improves their compatibility with other fediverse software.